Valves having sliding metal seals are well known for their resistance to contamination induced leakage. The shearing action of the hard metal seal edges of slide valves excludes fluid born contamination and accomplishes efficient sealing under circumstances which would interfere with the sealing capabilities of poppet valves and thereby allow leakage to occur.
A major disadvantage of valve mechanisms having sliding metal seals is the large frictional forces to which the valve mechanism is ordinarily subjected. The seals of poppet valves may be pressure balanced so that the valve operator (i.e., solenoid, spring, or pilot piston), has very low forces to overcome when shifting the position of the valve member. Large frictional forces cause larger power consumption of the valve actuator and also cause greater hysteresis to occur.
Solenoid energized valve mechanisms are typically employed for subsea control of oil and gas wells. The solenoids of solenoid valve mechanisms are energized by electrical energy transmitted through long power cables that extend from a surface based power source to the location of the valves. Typically, these long power cables have limited electrical transmission capacity because the size of the electrical conductors is limited and the length of these power cables subjects the electrical power to considerable line loss. Since subsea solenoid valves for well control are inaccessible from the standpoint of service, high reliability (i.e. contamination resistance) is of considerable importance.
Principally, the key to reducing the frictional forces to which a sliding seal valve is subjected, and hence the disadvantages of sliding metal seals is the reduction of the area of the sliding seals that is exposed to pressure. A point of diminishing practicality is soon reached with the traditional methods of reducing the pressure responsive area of valves of this particular type. A narrower contact surface seal reduces the pressure responsive area, but only at the risk of reduced structural integrity and reduced flow path dimension. A smaller diameter seal reduces the pressure responsive area but encounters additional difficulties because of the very small manufacturing and alignment tolerances that are presented.
The present invention has as its principal object, the provision of a novel sliding seal mechanism for valves which provides order of magnitude frictional force reduction as compared to conventional sliding seal type valve assemblies, while maintaining adequate seal contact surface dimension and while also providing simplicity of manufacture and alignment.
It is an even further feature of this invention to provide a novel seal arrangement for sliding seal type valve mechanism which includes a "rockable" mounting of the sliding seal assembly to insure that the sealing surface always maintains precision alignment and sealing capability as the sliding seal mechanism is reciprocated within the valve chamber of the valve.
It is also a feature of this invention to eliminate the need for conventional O-ring packings and to insure that the small seal diameter is sealed by means of an internal plug shaped elastomer seal packing that eliminates the need for close tolerance glands.